A distributor is an apparatus, which includes a rotor and ignition signal generating means consisting of a pick-up, a chopper, etc., for generating ignition signal in response to rotation of the rotor, for supplying ignition voltage to each of the plugs at a best timing. For that purpose the rotor is usually rotated by a cam-shaft or the like synchronously with the rotation of the engine, and the timing of ignition is therefore determined by means of adjusting the phase of the ignition signal generating means against the rotor.
As a concrete way of adjusting the phase of the ignition signal generating means against the rotor it has been recognized to be practicable to make the whole of a distributor housing rotate in relation to the rotor. For that reason it has been traditionally executed to rotatably fit a cylindrical portion of the distributor housing, through which a shaft of the rotor is pierced, into a fitting hole formed in a part of the engine, to form an elongated hole in a flange extended laterally from the cylindrical portion, and to rotate the housing about the cylindrical portion as far as the ignition timing may be adjusted, before a bolt pierced through the elongated hole is screwed up so that the housing may be fixed at a best suitable phase.
This determination or adjustment of the ignition timing is executed on full consideration of driving efficiency of the engine as well as diminishing of concentration of the harmful or toxic gas contained in the exhaust gas from the engine, so it requires fairly large scale equipment therefor and high technical skill. It is therefore highly desirable that the once settled position of the distributor will not be changed easily or unexpectedly.
A most suitable ignition timing only from the view point of driving efficiency of the engine is not necessarily equal to or agreeable with a most suitable ignition timing viewed from the driving efficiency of the engine and the diminishing of concentration of the toxic gas in the exhaust gas in parallel. In a case wherein the driving efficiency of the engine can be enhanced at the sacrifice of increasing the concentration of the toxic gas, it can happen that users of cars intentionally change the phase of the distributor. In some countries car makers are therefore said to be restricted or regulated to take a necessary measure by laws not to allow the users to easily change the phase of the distributor.